Weightlessness is experienced by people during free-fall. Colin Michael Foale, CBE, PhD, (born 6 January 1957) is an Anglo - American Astrophysicist and a NASA Free fall is motion with no Acceleration other than that provided by Gravity. Although the term 'zero gravity' is often used as a synonym, weightlessness in orbit is not the result of gravity itself being eliminated or even reduced significantly (in fact, the acceleration towards earth due to gravity at an altitude of 100 km is only 3% less than at the earth's surface. Gravitation is a natural Phenomenon by which objects with Mass attract one another ) Weightlessness (roughly speaking) occurs when a body (e. g. a person) is: falling freely; in orbit; in outer space (far from a planet, star, or other massive body); in an airplane following a particular parabolic flight path (e. g. the "Vomit Comet"); or one of several other (even more unusual) frames of reference. Vomit Comet is a nickname for any Airplane that briefly provides a nearly weightless environment in which to train Astronauts conduct research and

More generally, weightlessness occurs when a person (or object) is subject (at most) to the single non-contact force of gravity (or is not acted upon by any accelerating force), vs. the far more typical (in human experience) cases in which a contact force is acting—such as:

• standing on the ground, sitting in a chair on the ground, etc. (gravity is countered by the reaction force of the ground);
• flying in a plane (gravity is countered by the lift the wings provide) - see below for special trajectories which form an exception;
• atmospheric reentry, use of a parachute: atmospheric drag decelerates the vehicle;
• during an orbital maneuver in a spacecraft, or during the launch phase: the rocket provides thrust. In the context of a Fluid flow relative to a body the lift force is the component of the Aerodynamic force that is Perpendicular to the flow Trajectory is the path a moving object follows through space The object might be a Projectile or a Satellite, for example A parachute is a device used to slow the motion of an object through an atmosphere by creating drag. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a In Spaceflight, an orbital maneuver is the use of propulsion systems to change the Orbit of a Spacecraft. A spacecraft is a Vehicle or machine designed for Spaceflight. A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the Thrust is a reaction force described quantitatively by Newton 's Second and Third Laws.

(The principal difference is that gravity is a field force acting directly on a person and/or other bodies, just like on the vehicle's mass—whereas forces like atmospheric drag and thrust act through contact on the vehicle body itself (and are transmitted, in turn, through the contact between the vehicle and the person). In the first case the person and the vehicle floor are not 'pushed' towards one another; in the other cases, the force is transmitted through the vehicle's structure to the person and/or contents. )

Contents 1 Overview 2 Terminology 2.1 Zero gravity 2.2 Microgravity 3 Reduced weight 3.1 Reduced weight aircraft 3.1.1 NASA's C-9 aircraft 3.1.2 Zero Gravity Corporation 3.1.3 European Space Agency A300 Zero-G 3.1.4 Others 3.2 Ground-based reduced weight facilities 3.2.1 NASA drop facilities 3.2.2 Other facilities worldwide 3.3 Reduced weight in pilot training 4 Neutral buoyancy 5 Weightlessness in a spaceship 6 Weightlessness in the center of a planet 7 Health effects 8 Effects on non-human organisms 9 See also 10 Notes 11 External links

Overview

What humans perceive as "weight" is not actually the force of gravity pulling us towards the ground (actually, towards the center of the Earth—although this is the technical definition of "weight"). In Physics, a force is whatever can cause an object with Mass to Accelerate. Gravitation is a natural Phenomenon by which objects with Mass attract one another What we feel as "weight", is actually the normal reaction force of the ground (or whatever surface we are supported by) "pushing" upwards against us to counteract gravity's downward pull—that is: the "apparent weight". Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the (In the remainder of this article, the term 'weight', without 'apparent', is used in this sense. ) While this is not always intuitive, imagine the floor dropping out from under you: without it, you'd be falling—and experiencing weightlessness. It's the floor supporting you against gravity's pull—and which keeps you from falling to the center of the Earth—that creates the sensation of "weight".

For example: a person in a broken lift in free-fall "experiences" weightlessness. Free fall is motion with no Acceleration other than that provided by Gravity. This is because there is no force from the lift's floor on the person's feet, against the pull of gravity, as both the lift and the person are being pulled down with the same acceleration. When the lift is at rest on the ground, however, the force of gravity pulling downwards on the person is exactly matched (in the opposite direction, and by the same amount) by the support of the lift floor.

Because the person's skeleton is solid, each horizontal cross section of the person experiences not only the force due to gravity on it, but also the weight of whatever portion of the person is above it. (In the case of an object, or portion thereof, which is not supported from below, but suspended from above, a 'negative pressure', or tension gradient exists. It occurs because each cross section of a hanging object, a rope for instance, must support the weight of every piece below it. ) Part of feeling "weight", then, is actually experiencing such a pressure/tension gradient within one's own body parts (e. g. : while standing on one foot, the foot on the ground would feel the pressure of the entire body's weight, whereas the other leg and both arms would feel/be subjected to the tension gradients of their own weight being pulled down against their sockets).

In free-fall, a person or object experiences no measurable (or apparent) weight because all parts of the object are accelerating uniformly (any variations in acceleration due to tidal forces being imperceptible). The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced

Terminology

Zero gravity

Often, the term 'zero gravity' or 'reduced gravity' is used to describe weightlessness, but these are scientifically inaccurate. A spacecraft and its contents are kept in orbit by the gravity of the body it orbits; that they are all subject to roughly the same gravity is the reason for the weightlessness. James Oberg explains:^[1]

The myth that satellites remain in orbit because they have "escaped Earth's gravity" is perpetuated further (and falsely) by almost universal use of the zingy but physically nonsensical phrase "zero gravity" (and its techweenie cousin, "microgravity") to describe the free-falling conditions aboard orbiting space vehicles. James Edward Oberg (born 1944 (often known as Jim Oberg) is an American Space Journalist and Historian, regarded as an expert on Of course, this isn't true; gravity still exists in space. It keeps satellites from flying straight off into interstellar emptiness. What's missing is "weight", the resistance of gravitational attraction by an anchored structure or a counterforce. Satellites stay in space because of their tremendous horizontal speed, which allows them--while being unavoidably pulled toward Earth by gravity--to fall "over the horizon. " The ground's curved withdrawal along the Earth's round surface offsets the satellites' fall toward the ground. Speed, not position or lack of gravity, keeps satellites up, and the failure to understand this fundamental concept means that many other things people "know" just ain't so.

Microgravity

The term 'microgravity' is also used because weightlessness in e. g. a spaceship or other container is not perfect. Causes in Earth orbit include:

• Centripetal gravity decreases 1 ppm for every 3 m increase in altitude. "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly Objects that are not points will feel a tidal force, a differential pull on their various parts. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced
• In a spaceship in orbit the centrifugal force is likewise higher at the upper side. (This is also the tidal force. )
• Objects left alone will "fall" toward the densest part of the spacecraft. When they eventually touch the spacecraft, they will stop moving and feel weight.
• Though very thin, there is some air at the level of the Space Shuttle's orbit height of 185 to 1,000 km, which causes deceleration due to friction. NASA 's Space Shuttle, officially called the Space Transportation System ( STS) is the Spacecraft currently used by the United States This is perceived as "weight" in the direction of motion. Above 10,000km, this fades into negligibility compared to solar wind. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun.
• Left to themselves, different parts of a vehicle either side of its orbital plane are in their own orbital planes. In the frame of reference of the vehicle, this pushes objects inwards towards the orbital plane of the vehicle as a whole.

The microgravity symbol, µg, was used on the insignia of the Space Shuttle flight STS-107, because this flight was devoted to microgravity research (see picture in that article). NASA 's Space Shuttle, officially called the Space Transportation System ( STS) is the Spacecraft currently used by the United States STS-107 was a Space shuttle mission by NASA using the Space Shuttle Columbia, launched January 16, 2003.

Reduced weight

Reduced weight aircraft

NASA's C-9 aircraft

NASA's C-9 Reduced Gravity Aircraft is based at Lyndon B. Johnson Space Center and affectionately called the "vomit comet". The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Vomit Comet is a nickname for any Airplane that briefly provides a nearly weightless environment in which to train Astronauts conduct research and The Lyndon B Johnson Space Flight Center ( "JSFC") is the National Aeronautics and Space Administration 's center for Vomit Comet is a nickname for any Airplane that briefly provides a nearly weightless environment in which to train Astronauts conduct research and It is an airplane that NASA flies in 6 mile long parabolic arcs, first climbing in altitude, then falling, in such a way that the flight path and speed correspond to that of an object without propulsion and not experiencing air friction. In Mathematics, the parabola (pəˈræbələ from the Greek παραβολή) is a Conic section, the intersection of a right circular Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e This is realized by propulsion and steering such that air friction is compensated and nothing else. The result is that people inside are not pushed towards the bottom or any other side of the plane, i. e. they are temporarily weightless, each time for a period of 25 seconds. Typically one flight lasts about two hours, in which 40 parabolas are flown.

NASA's Microgravity University - Reduced Gravity Flight Opportunities Plan, also known as the Reduced Gravity Student Flight Opportunities Program, allows teams of undergraduates to submit a microgravity experiment proposal. Microgravity University, also known as the Reduced Gravity Student Flight Opportunities Program (RGSFOP is a program run by NASA which enables undergraduate university If selected, the teams design and implement their experiment, and students are invited to fly on NASA's McDonnell Douglas C-9. McDonnell Douglas was a major American Aerospace manufacturer and Defense contractor, producing a number of famous commercial and military aircraft WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout The aircraft flies in the pattern described above, so that the experiment has around 20 to 25 seconds (each parabola) to perform its function in microgravity.

Zero Gravity Corporation

The Zero Gravity Corporation operates a modified Boeing 727 which flies parabolic arcs similar to those of NASA's Reduced Gravity Aircraft. Zero Gravity Corporation (also known as ZERO-G) is a Nevada -based company formerly of Fort Lauderdale which operates weightless flights WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Flights may be purchased for both tourism and research purposes.

European Space Agency A300 Zero-G

The European Space Agency flies parabolic flights on a specially-modified Airbus A300 aircraft, in order to research microgravity. The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout The ESA flies campaigns of three flights on consecutive days, each flight flying about 30 parabolas, for a total of about 10 minutes of weightlessness per flight. The ESA campaigns are currently operated from Bordeaux - Mérignac Airport in France by the company Novespace,^[2] while the aircraft is operated by the Centre d'essais en Vol (CEV - French Test Flight Centre). Bordeaux - Mérignac Airport (Aéroport de Bordeaux - Mérignac is an Airport serving the French city of Bordeaux. This article is about the country For a topic outline on this subject see List of basic France topics. The first ESA Zero-G flights were in 1984, using a NASA KC-135 aircraft in Houston, Texas. As of March 2006, the ESA has flown 43 campaigns. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Other aircraft it has used include the Russian Ilyushin Il-76 MDK and French Caravelle. Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout ^[3][4][5]

Others

In Austria, a company called Paul's Parabelflug offers parabolic flights, but they are prohibited from offering zero-g flights, and now offer only Martian and lunar gravity flights.

A company in Hungary briefly offered parabolic flights, but went out of business after only a few flights.

A Swedish company, Xero, planned to fly parabolic flights with the mammoth Ilyushin Il-76, but the person in charge of the project left the company, and the project was cancelled. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout

Ground-based reduced weight facilities

Ground-based facilities that produce reduced-weight conditions for research purposes are typically referred to as drop tubes or drop towers. Drop Tower, formerly known as Drop Zone Stunt Tower, are thrill rides of varying sizes but all of the same name owned by five Cedar Fair parks

NASA drop facilities

NASA's Zero Gravity Facility, located at the Glenn Research Center in Cleveland, Ohio, is a 145-meter vertical shaft, largely below the ground, with an integral vacuum drop chamber, in which an experiment vehicle can have a free fall for a duration of 5. NASA John H Glenn Research Center at Lewis Field (see History for previous names is a NASA center located within the cities of Brook Park Cleveland is a City in the US state of Ohio and the County seat of Cuyahoga County, the most populous county in the state Drop Tower, formerly known as Drop Zone Stunt Tower, are thrill rides of varying sizes but all of the same name owned by five Cedar Fair parks 18 seconds, falling a distance of 132 meters. The experiment vehicle is stopped in approximately 4. 5 meters of pellets of expanded polystyrene and experiences a peak deceleration rate of 65g. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene

Also at NASA Glenn is the 2. 2 Second Drop Tower, which has a drop distance of 24. 1 meters. Experiments are dropped in a Drag Shield, in order to reduce the effects of air drag. The entire package is stopped in a 3. 3 meter tall air bag, at a peak deceleration rate of approximately 20g. While the Zero Gravity Facility conducts one or two drops per day, the 2. 2 Second Drop Tower can conduct up to twelve drops per day.

NASA's Marshall Space Flight Center hosts another drop tube facility that is 105 meters tall and provides a 4. George C Marshall Space Flight Center (MSFC the original home of NASA, is a lead center for propulsion, Space Shuttle propulsion Shuttle external fuel Drop Tower, formerly known as Drop Zone Stunt Tower, are thrill rides of varying sizes but all of the same name owned by five Cedar Fair parks 6 second free fall under near-vacuum conditions. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. ^[6]

Humans cannot utilize these gravity shafts, as the deceleration experienced by the drop chamber would likely kill or seriously injure anyone using them; 20 g is about the highest deceleration that a fit and healthy human being can withstand momentarily without sustaining permanent injury.

Other facilities worldwide

• Micro-Gravity Laboratory of Japan (MGLAB) - 4. 5 s free fall
• Experimental drop tube of the metallurgy department of Grenoble - 3. Drop Tower, formerly known as Drop Zone Stunt Tower, are thrill rides of varying sizes but all of the same name owned by five Cedar Fair parks Grenoble is a city and commune in south-east France situated at the foot of the Alps where the Drac joins the Isère River. 1 s free fall
• Fallturm Bremen University of Bremen in Bremen. Fallturm Bremen is a Drop tower at the Center of Applied Space Technology and Microgravity at the University of Bremen in Bremen. The University of Bremen ( German Universität Bremen) is a university of approximately 23500 people from 126 countries that are studying teaching researching and Bremen (ˈbʁeːmən is a Hanseatic city in northwestern Germany (official name Stadtgemeinde Bremen / City Municipality of Bremen - 4. 74 s free fall

Reduced weight in pilot training

People have differing reactions to reduced weight sensations, and these can compromise flight safety if an aircraft pilot is not trained to respond properly, particularly in an emergency. Normally in flight training, flight instructors will gradually introduce reduced weight maneuvers, while carefully monitoring the student pilot. Flight training is a course of study used when learning to pilot an Aircraft. A flight instructor is a person who teaches others to fly Aircraft. Most students become accustomed to the sensation and are able to perform satisfactorily with some training. Students who are not able to overcome their anxiety will not be able to complete flight training. ^[7]

Neutral buoyancy

Weightlessness can also be simulated with the use of neutral buoyancy, in which human subjects and equipment are placed in a water environment and weighted or buoyed until they hover in place. Neutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium NASA uses neutral buoyancy to prepare for EVAs at its Neutral Buoyancy Laboratory. Extra-vehicular activity ( EVA) is work done by an Astronaut away from the Earth and outside of a Spacecraft. The Neutral Buoyancy Laboratory (NBL is an Astronaut training facility located at the Sonny Carter Training Facility and maintained by NASA 's Neutral buoyancy is also used for EVA research at the University of Maryland's Space Systems Laboratory, which operates the only neutral buoyancy tank at a college or university. The University of Maryland College Park (often referred to as The University of Maryland UMD, UMCP or simply Maryland) is a public research The Space Systems Laboratory ( SSL) is part of the Aerospace Engineering Department and A

It is important to note that neutral buoyancy is not weightlessness. While both experiences feature floating, astronauts who are doing neutral buoyancy training still feel their full body weight within their spacesuit. In orbit, an astronaut's body weighs nothing at all.

Weightlessness in a spaceship

Long periods of weightlessness occur in a spaceship outside a planet's atmosphere, provided no propulsion is applied and the ship is not rotating. Marsha Sue Ivins (born 15 April 1951) is an American Astronaut and a veteran of five Space shuttle missions STS-98 was a Space Shuttle mission to the International Space Station (ISS flown by Space Shuttle '' Atlantis''. A spacecraft is a Vehicle or machine designed for Spaceflight. This is the case when orbiting the earth (except when rockets fire for orbital maneuvers), but not during atmospheric re-entry. In Spaceflight, an orbital maneuver is the use of propulsion systems to change the Orbit of a Spacecraft. Weightlessness does not occur in a rocket ship that is accelerating by firing its rockets. A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the Even if the rocket accelerates uniformly, the force is applied to the back end of the rocket by the escaping gas and that force is transferred throughout the ship via pressure or tension, precluding weightlessness. Weightlessness in a spaceship or space station is achieved by free-fall. The ship and all things in it are literally falling toward the Earth's surface, but their speed in orbit around the Earth allows for almost perpetual falling.

Weightlessness in the center of a planet

In the center of a planet a person would feel weightless because the pull of the surrounding mass of the planet would cancel out. More generally, the gravitational force is zero everywhere within a hollow spherically symmetrical planet, by the shell theorem. Hollow Earth is a belief that the planet Earth has a hollow interior and possibly a habitable inner surface In Classical mechanics, the shell theorem gives gravitational simplifications which can be applied to objects inside or outside a spherically symmetrical body

Health effects

Following the establishment of orbiting stations that can be inhabited for long durations by humans, exposure to weightlessness has been demonstrated to have some deleterious effects to health. A space station is an artificial structure designed for Humans to live in Outer space. Humans are well-adapted to the physical conditions prevailing at the surface of the Earth. When weightless, certain physiological systems begin to alter and temporary and long term health issues can occur.

The most common initial condition experienced by humans after the first couple of hours or so of weightlessness is known as space adaptation syndrome or SAS, commonly referred to as space sickness. Space adaptation syndrome (SAS or space sickness, is a condition experienced by around half of Space travelers during adaptation to Microgravity. The symptoms include general queasiness, nausea, vertigo, headaches, lethargy, vomiting, and an overall malaise. Nausea ( Latin: Nausea, Greek:, " Sea-sickness " also called wamble) is the sensation of unease and discomfort Vertigo (from the Latin vertere, to turn and the suffix -igo, a condition i A headache ( cephalalgia in medical terminology is a condition of pain in the Head; sometimes Neck or upper back pain may also be interpreted Vomiting (also called throwing up, emesis) is the forceful expulsion of the contents of one's Stomach through the Mouth and sometimes the The first case was reported by cosmonaut Gherman Titov in 1961. Gherman Stepanovich Titov (Герман Степанович Титов ( September 11, 1935 &ndash September 20, 2000) was a Soviet Since then roughly 45% of all people to experience free floating under zero gravity have also suffered from this condition. The duration of space sickness varies, but in no case has it lasted more than 72 hours. By that time the astronauts have grown accustomed to the new environment. NASA measures SAS using the "Garn scale", named for United States Senator Jake Garn, whose SAS during STS-51-D was so severe as to be ranked 13 on this scale. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program The United States Senate is the Upper house of the bicameral United States Congress, the Lower house being the House of Representatives Edwin Jacob Garn (born October 12, 1932) is an American politician a member of the Republican Party, and served as a U STS 51-D was the sixteenth flight of a space shuttle and the fourth flight of ''Discovery''.

The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia; these effects can be minimized through a regimen of exercise. Muscle atrophy is defined as a decrease in the mass of the muscle it can be a partial or complete wasting away of muscle In Biology, the skeleton is a strong and often a rigid framework that supports the body of an animal holding it upright and giving it shape and strength (Also skeletal Spaceflight osteopenia refers to the characteristic Bone loss that occurs during Spaceflight. Other significant effects include fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. This is an article about the rock music band "Circulatory System" Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, excess flatulence, and puffiness of the face. Flatulence is the production of a mixture of gases in the digestive tract of Mammals that are byproducts of the digestion process These effects are reversible upon return to Earth.

Many of the conditions caused by exposure to weightlessness are similar to those resulting from aging. Scientists believe that studies of the detrimental effects of weightlessness could have medical benefits, such as a possible treatment for osteoporosis and improved medical care for the bed-ridden and elderly. Osteoporosis is a Disease of Bone that leads to an increased risk of fracture.

Effects on non-human organisms

Russian scientists have observed differences between cockroaches conceived in space and their terrestrial counterparts. The space-conceived cockroaches grew more quickly, and also grew up to be faster and tougher. ^[8]

Fowl eggs which are fertilized in microgravity may not develop properly. ^[9]

See also

• Artificial gravity
• Human adaptation to space
• Microgravity University
• Vomit Comet

Notes

1. ^ Oberg, James (May 1993). Artificial gravity is a simulation of gravity in Outer space or Free-fall. Human physiological adaptation to space is a challenge faced in developing Human spaceflight. Microgravity University, also known as the Reduced Gravity Student Flight Opportunities Program (RGSFOP is a program run by NASA which enables undergraduate university Vomit Comet is a nickname for any Airplane that briefly provides a nearly weightless environment in which to train Astronauts conduct research and James Edward Oberg (born 1944 (often known as Jim Oberg) is an American Space Journalist and Historian, regarded as an expert on "Space myths and misconceptions". Omni 15 (7).  
2. ^ Novespace: microgravity, airborne missions
3. ^ European Space Agency. The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member A300 Zero-G. ESA Human Spaceflight web site. Retrieved on 2006-11-12. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 764 - Tibetan troops occupy Chang'an, the capital of the Chinese Tang Dynasty, for fifteen days
4. ^ European Space Agency. The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member Next camaign. ESA Human Spaceflight web site. Retrieved on 2006-11-12. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 764 - Tibetan troops occupy Chang'an, the capital of the Chinese Tang Dynasty, for fifteen days
5. ^ European Space Agency. The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member Campaign Organisation. ESA Human Spaceflight web site. Retrieved on 2006-11-12. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 764 - Tibetan troops occupy Chang'an, the capital of the Chinese Tang Dynasty, for fifteen days
6. ^ Marshall Space Flight Center Drop Tube Facility
7. ^ Reduced G Familiarization from Gliding New Zealand.
8. ^ Mutant super-cockroaches from space. New Scientist (January 21, 2008).
9. ^ Egg Experiment in Space Prompts Questions. New York Times (1989-03-31). Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar) Events 307 - After divorcing his wife Minervina, Constantine marries Fausta, the daughter of the retired Roman Emperor

External links

• Criticism of the terms "Zero Gravity" and "Microgravity", a persuasion to use terminology that reflects accurate physics (Sci. space post).
• Zero-G Research Facility, a NASA facility for ground-based microgravity research. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program
• Microgravity flights on board the Airbus A300 Zero-G
• NASA Microgravity University, a NASA student program that allows teams of college students to plan a microgravity experiment and fly on board NASA's C-9. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout
• maniacworld.com "NASA Reduced Gravity Aircraft", videos of the NASA Reduced Gravity Aircraft and of participants in a flight on that aircraft.

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